Method for Producing a Gun Cartridge Casing

ABSTRACT

The present invention relates to a novel method for producing a gun cartridge casing in a single multiple station deep drawing transfer press.

FIELD OF THE INVENTION

The present invention relates to a novel method for producing a gun cartridge casing.

BACKGROUND OF THE INVENTION

Typically gun cartridge cases are drawn from sheet metal discs in three ‘stages’. First a cup is formed from the sheet metal disc. Thereafter the cup is drawn to the desired length by a number of forming operations through punches of decreasing diameters until a suitable length of the part is attained. The drawn part is then provided with a neck, if necessary. Finally, the bottom of the drawn and necked part is provided with a groove to form the final cartridge case.

After each drawing stage the parts are annealed, pickled, rinsed and subjected to further quality improvement measures.

For the annealing process the part should be clean, which requires a washing before the annealing. After the annealing the part is pickled, bondered and/or lubricated, which is required for the following drawing operations.

Depending on the calibre, the drawing process is typically carried out in a transfer press, where the product is deep drawn in a number of sets comprising pairs of punches and dies (stations) to receive workpieces leaving a deep drawn tool. If the drawing is carried out in a transfer press, the transport is accomplished by using mechanical grippers.

Normally a transfer press comprises 5 to 12 stations. Due to the heavy reduction in strength of the sheet, usually from an initial strength of about 3 to 4 mm to final strength of about 0.3 mm, the material is hardened. Further, the forming capability is reduced with every step. Therefore, the processes according to the state of the art require at least one further intermediate annealing process (incl. washing and pickling), sometimes depending on the calibre even more.

After the ironing process in the transfer press there is necking process for most of the rifle cartridges. The necking is done after an annealing process to reduce the material stress before this critical forming process. Typically the necking is done in 2 stations.

The groove and trim are formed using special equipment, which is separate from transfer press. For this to be achieved, the case is fixed in a collet chuck and turned while a shaped turning tool cuts the groove and a second one trims the length.

It will readily be realised that such processes are laborious, costly, and require costly investments.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a method for producing a gun cartridge casing which can be performed on a single transfer press.

There is provided a method for manufacturing a gun cartridge casing comprising the steps of:

-   -   (a) providing a metal sheet to a multiple station deep drawing         transfer press which comprises a blanking device for cutting         blanks out of the metal sheet;     -   (b) cutting a metal blanket of said metal sheet;     -   (c) transferring said metal blanket obtained in step (b) to a         first forming station which comprises a punch and a die, wherein         said metal disc sheet is formed into a metal cup;     -   (d₁) transferring said metal cup obtained in step (c) to a         second set of forming stations comprising a number of punches         and dies, wherein said metal cup is deep drawn into an cartridge         case; and     -   (e₁) releasing said cartridge case from the multiple station         deep drawing transfer press,         wherein between steps (a) and (e₁), there are no intermediate         washing, pickling and/or bondering steps.

In an embodiment of the invention, the steps (b) of producing a blank from a metal sheet, and (c) of producing a cup are carried out in one cutting and forming station.

If the cartridge case is to be provided with a groove, it is advantageously produced in a method for manufacturing a gun cartridge casing having a groove in a single multiple station deep drawing transfer press comprising the steps of:

-   -   (d₂) providing a metal cup to a set of forming stations in a         multiple station deep drawing transfer press comprising a number         of punches and dies, wherein said metal cup is deep drawn into a         cartridge case; and     -   (e₂) transferring said metal cup obtained from step (d₂) to a         further forming station comprising a punch and a die, wherein         the diameter of the bottom of said cartridge case is reduced to         the required groove diameter;     -   (f₁) transferring said cartridge case having a bottom of reduced         diameter obtained in step (e₂) to a further forming station         comprising a punch and a die to form a groove, wherein the die         is a splitted die which can be opened after operation; and     -   (g₁) opening the splitted die and releasing the cartridge case         provided with a groove from the multiple station deep drawing         transfer press,         wherein between steps (d₂) and (g₁), there are no intermediate         washing, pickling and/or bondering steps.

Preferably, also the steps of cutting blanks of a metal sheet and forming a cup of the metal sheet are carried out in the same multiple station deep drawing transfer press in a sequence comprising the following steps:

-   -   (a) providing a metal sheet to a multiple station deep drawing         transfer press which comprises a blanking device for cutting         blanks out of the metal sheet;     -   (b) cutting a metal blanket of said metal sheet;     -   (c) transferring said metal blanket obtained in step (b) to a         first forming station which comprises a punch and a die, wherein         said metal disc sheet is formed into a metal cup;         whereupon the cup is transferred to step (d₂), wherein between         steps (a) and (g₁), there are no intermediate washing, pickling         and/or bondering steps.

Some cartridge cases, particularly those used in rifles, require the presence of a neck. Also the neck is advantageously produced within the same multiple station deep drawing transfer press after step in a method for manufacturing a gun cartridge casing having a neck in a single multiple station deep drawing transfer press comprising the steps of:

-   -   (d₃) providing a metal cup to a set of forming stations in a         multiple station deep drawing transfer press comprising a number         of punches and dies, wherein said metal cup is deep drawn into a         cartridge case; and     -   (e₃) transferring said cartridge case obtained in step (d₃) to a         further forming station, wherein said cartridge case is provided         with a neck;     -   (f₂) and releasing the cartridge case from the multiple station         deep drawing transfer press,         wherein between steps (d₃) and (f₂), there are no intermediate         washing, pickling and/or bondering steps.

Preferably, also the steps of cutting blanks of a metal sheet and forming a cup of the metal sheet are carried out in the same multiple station deep drawing transfer press in a sequence comprising the following steps:

-   -   (a) providing a metal sheet to a multiple station deep drawing         transfer press which comprises a blanking device for cutting         blanks out of the metal sheet;     -   (b) cutting a metal blanket of said metal sheet;     -   (c) transferring said metal blanket obtained in step (b) to a         first forming station which comprises a punch and a die, wherein         said metal disc sheet is formed into a metal cup;         whereupon the cup is transferred to step (d₃), wherein between         steps (a) and (f₂), there are no intermediate washing, pickling         and/or bondering steps.

If a cartridge case having a groove and a neck is to be produced, then it may be produced in a method for manufacturing a gun cartridge casing having a neck in a single multiple station deep drawing transfer press comprising the steps of:

-   -   (d₄) providing a metal cup to a set of forming stations in a         multiple station deep drawing transfer press comprising a number         of punches and dies, wherein said metal cup is deep drawn into a         cartridge case; and     -   (e₄) transferring said cartridge case obtained from step (d₄) to         a further forming station comprising a punch and a die, wherein         the bottom of said cartridge case is reduced to the required         groove diameter;     -   (f₃) transferring said cartridge case provided with a reduced         bottom obtained in step (e₂) to a further forming station         comprising a punch and a die to form a groove, wherein the die         is a splitted die which can be opened after operation; and;     -   (g₂) opening the splitted die and transferring said cartage case         provided with a groove obtained in step (f₂) to a further         forming station, wherein said elongated metal cup is provided         with a neck; and     -   (h₁) releasing the cartridge case from the multiple station deep         drawing transfer press         wherein between steps (d₄) and (h₁), there are no intermediate         washing, pickling and/or bondering steps.

Preferably, also the steps of cutting blanks of a metal sheet and forming a cup of the metal sheet are carried out in the same multiple station deep drawing transfer press in a sequence comprising the following steps:

-   -   (a) providing a metal sheet to a multiple station deep drawing         transfer press which comprises a blanking device for cutting         blanks out of the metal sheet;     -   (b) cutting a metal blanket of said metal sheet;     -   (c) transferring said metal blanket obtained in step (b) to a         first forming station which comprises a punch and a die, wherein         said metal disc sheet is formed into a metal cup;         whereupon the cup is transferred to step (d₄), wherein between         steps (a) and (h₁), there are no intermediate washing, pickling         and/or bondering steps.

If the cartridge case is to be equipped with a neck, such as in many rifle cartridge cases, it is desirable to produce it in the same multiple station deep drawing transfer press as all previous steps. In said machine, the neck is preferably produced at the very end of the process. Pistol cartridge cases are normally not provided with a neck.

A forming station in the multiple station deep drawing transfer press usually comprises a pair of a punch and a die where the metal sheet is formed, first into a metal cup, and subsequently into a cartridge case with elongated form in relation to the metal cup, a stripper, an ejecter and a gripper which transports the cup of cartridge case from one forming station to the next one. In case a neck is formed, the forming station does not comprise a punch. There is just a die which forms a neck on the open side of the cartridge case and an inner pilot to maintain the wall thickness.

According to the present invention there is also provided a multiple station deep drawing transfer press for manufacturing a gun cartridge casings in a single machine, which comprises a cutting device for cutting discs out of a metal sheet and a number of forming stations for drawing and forming said metal discs, wherein in at least one forming station comprising a punch and a die, the die exhibits a splitted punch to form a groove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-sectional view of a splitted punch in a closed state in accordance with the present invention.

FIG. 2 depicts a cross-sectional view of a splitted punch in an open state in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, the metal sheet, which is preferably a brass sheet, is fed directly into a deep drawing transfer press. Preferably a zig-zag feeder for providing a multiple cut is used to feed the material to the cutting tool which cuts discs out of sheet metal. A zig-zag feeder will utilize the material in a most efficient manner without needless waste of material.

Thereafter, a cup is formed in the transfer press, and the cup is transferred to subsequent stations of the transfer press, preferably without any intermediate washing, pickling and/or bondering. During various forming steps, the wall thickness of the case is reduced to a final wall thickness.

To allow the further deep drawing and ironing operations without any annealing process to the final wall thickness, a reduction of the true strain of per operation is required. Preferably, according to the process of the present invention, the number of forming stations (pairs of punches and dies) is higher than in known processes. Preferably, the multiple station deep drawing transfer press used in the method according to the present invention comprises 12 to 25, preferably 15 to 25 forming stations in total. For Example, to include a neck, without any intermediate annealing step, the number of forming stations used for step (e₃) is preferably from three to seven, most preferably from four to five.

In step (c) the cup is preferably formed in one forming station, where the thickness of the metal is preferably reduced by 40% to 70% while a cup is formed.

Preferably, the number of forming stations for carrying out drawing and forming steps (d) of the cup to form a cartridge case is from three to nine, more preferably from four to eight, such as from five to seven. In these forming stations, the wall thickness of the cup or of the intermediately drawn cases is preferably reduced by a higher percentage during the earlier stages of the drawing process of step (d) than in later stages of the step (d). For Example, according to a preferred embodiment the wall thickness of the cup is reduced by 30% to 50%, more preferably about 40% in a first forming station of step (d). While normally the reduction is about 60% to 70%.

According to a further preferred embodiment, the wall thickness of the drawn case is reduced in a second forming station of step (d) by a lower percentage than in a first forming station of step (d). Preferably, the wall thickness of the drawn case is reduced by 20% to 30% in a second forming station of step (d).

According to a still further preferred embodiment, the wall thickness of the drawn case is reduced in a third forming station of step (d) by a lower percentage than in a second forming station of step (d). Preferably, the wall thickness of the drawn case is reduced by 10% to 25%, preferably 10% to 20% in a third forming station of step (d). While normally the reduction is about 25% to 35%.

According to a still further preferred embodiment, the wall thickness of the drawn case is reduced in a fourth and any further forming station of step (d) by an equal or a lower percentage than in a third forming station of step (d). Preferably, the wall thickness of the drawn case is reduced by 10% to 20% in a fourth or any further forming station of step (d).

With the increasing number of forming stations and therefore with increasing bed size, the forming and coining force increases which may result in a winkling of the punch. The press force, depending on the caliber of the gun cartridge case, is preferably chosen between 75 to 250 tons, and a bed length is preferably from of 1000 to 3000 mm. Preferably, a ridged mechanical press or ideally a servo spindle press is used, which can actively correct the punch winkling.

Preferably, one or two flash holes are pierced in the drawn case within the deep drawing transfer press.

As described above, according to the state of the art, the grooving process is typically carried out in an external operation, in a turning method, wherein material is removed from the blank. The method according to the present invention, however, for the first time integrates the grooving steps in a transfer press, and does not remove material while the groove is formed.

The groove is formed in two steps. For forming the groove, the first operation is a drawing operation where the bottom of the case is reduced in diameter to the required groove diameter. In a further station in the deep drawing transfer press, the bottom of the case is held with a splitted punch, then, the bottom and primer pocked are coined into the case. The material flows radially and, thus, the groove is formed. To release the case of the splitted punch, the punch is opened into its segments.

This is further demonstrated by appending FIGS. 1 and 2, which are a cross-sectional view of a splitted punch according to the present invention in closed state (FIG. 1), and in opened state (FIG. 2), respectively. 

1. A method for manufacturing a gun cartridge casing in a single multiple station deep drawing transfer press comprising the steps of: (a) providing a metal sheet to a multiple station deep drawing transfer press which comprises a blanking device for cutting blanks out of the metal sheet; (b) cutting a metal blanket of said metal sheet; (c) transferring said metal blanket obtained in step (b) to a first forming station which comprises a punch and a die, wherein said metal disc sheet is formed into a metal cup; (d1) transferring said metal cup obtained in step (c) to a second set of forming stations comprising a number of punches and dies, wherein said metal cup is deep drawn into an cartridge case; and (e1) releasing said cartridge case from the multiple station deep drawing transfer press, wherein between steps (a) and (e1), there are no intermediate washing, pickling and/or bondering steps.
 2. A method for manufacturing a gun cartridge casing having a groove in a single multiple station deep drawing transfer press comprising the steps of: (d2) providing a metal cup to a set of forming stations in a multiple station deep drawing transfer press comprising a number of punches and dies, wherein said metal cup is deep drawn into a cartridge case; and (e2) transferring said metal cup obtained from step (d2) to a further forming station comprising a punch and a die, wherein the diameter of the bottom of said cartridge case is reduced to the required groove diameter; (f1) transferring said cartridge case having a bottom of reduced diameter obtained in step (e2) to a further forming station comprising a punch and a die to form a groove, wherein the die is a splitted die which can be opened after operation; and (gi) opening the splitted die and releasing the cartridge case provided with a groove from the multiple station deep drawing transfer press, wherein between steps (d2) and (gi), there are no intermediate washing, pickling and/or bondering steps.
 3. The method according to claim 2, comprising the steps of: (a) providing a metal sheet to a multiple station deep drawing transfer press which comprises a blanking device for cutting blanks out of the metal sheet; (b) cutting a metal blanket of said metal sheet; (c) transferring said metal blanket obtained in step (b) to a first forming station which comprises a punch and a die, wherein said metal disc sheet is formed into a metal cup; whereupon the cup is transferred to step (d2), wherein between steps (a) and (gi), there are no intermediate washing, pickling and/or bondering steps.
 4. A method for manufacturing a gun cartridge casing having a neck in a single multiple station deep drawing transfer press comprising the steps of: (d3) providing a metal cup to a set of forming stations in a multiple station deep drawing transfer press comprising a number of punches and dies, wherein said metal cup is deep drawn into a cartridge case; and (e3) transferring said cartridge case obtained in step (d3) to a further forming station, wherein said cartridge case is provided with a neck; (f2) and releasing the cartridge case from the multiple station deep drawing transfer press, wherein between steps (d3) and (f2), there are no intermediate washing, pickling and/or bondering steps.
 5. The method according to claim 4, comprising the steps of: (a) providing a metal sheet to a multiple station deep drawing transfer press which comprises a blanking device for cutting blanks out of the metal sheet; (b) cutting a metal blanket of said metal sheet; (c) transferring said metal blanket obtained in step (b) to a first forming station which comprises a punch and a die, wherein said metal disc sheet is formed into a metal cup; whereupon the cup is transferred to step (d3), wherein between steps (a) and (f2), there are no intermediate washing, pickling and/or bondering steps.
 6. A method for manufacturing a gun cartridge casing having a neck in a single multiple station deep drawing transfer press comprising the steps of: (d4) providing a metal cup to a set of forming stations in a multiple station deep drawing transfer press comprising a number of punches and dies, wherein said metal cup is deep drawn into a cartridge case; and (e4) transferring said cartridge case obtained from step (d4) to a further forming station comprising a punch and a die, wherein the bottom of said cartridge case is reduced to the required groove diameter; (f3) transferring said cartridge case provided with a reduced bottom obtained in step (e2) to a further forming station comprising a punch and a die to form a groove, wherein the die is a splitted die which can be opened after operation; and; (g2) opening the splitted die and transferring said cartage case provided with a groove obtained in step (f2) to a further forming station, wherein said elongated metal cup is provided with a neck; and (h1) releasing the cartridge case from the multiple station deep drawing transfer press wherein between steps (d4) and (h1), there are no intermediate washing, pickling and/or bondering steps.
 7. The method according to claim 6, comprising the steps of: (a) providing a metal sheet to a multiple station deep drawing transfer press which comprises a blanking device for cutting blanks out of the metal sheet; (b) cutting a metal blanket of said metal sheet; (c) transferring said metal blanket obtained in step (b) to a first forming station which comprises a punch and a die, wherein said metal disc sheet is formed into a metal cup; whereupon the cup is transferred to step (d3), wherein between steps (a) and (h1), there are no intermediate washing, pickling and/or bondering steps.
 8. The method according to claim 1, wherein the metal sheet is of brass.
 9. The method according to claim 1, wherein said multiple station deep drawing transfer press comprises 12 to 25 pairs of punches and dies in total.
 10. The method according to claim 1, wherein said third set comprises three to five pairs of punches and dies for carrying out step (e).
 11. The method according to claim 1, wherein said multiple station deep drawing transfer press develops a press force between 75 and 250 tons.
 12. The method according to claim 1, wherein said multiple station deep drawing transfer press has a bed length between 1000 and 3000 mm.
 13. The method according to claim 1, wherein said multiple station deep drawing transfer press comprises a servo spindle press which actively corrects punch wrinkling.
 14. Multiple station deep drawing transfer press for manufacturing a gun cartridge casings in a single machine, which comprises a cutting device for cutting discs out of the metal sheet and a number of pairs of punches and dies for drawing said metal discs, wherein in at least one pair of a punch and a die, the die exhibits a splitted punch to form a groove.
 15. The method according to claim 9, wherein said multiple station deep drawing transfer press comprises 15 to 25 pairs of punches and dies in total. 